When your sphincter can no longer contain the gyser like forces in your colon and either matter or gas escapes in such a violent manner that it causes mass distress to everyone around.
1) I was walking by a friend's cubicle when he had an assplosion. I can still see all of my coworkers running much like Harrison Ford would run from a detonating bomb!
2) I was sitting in a stall when someone next to me assploded. The stench was so foul and the sound so wretched, I decided to just wipe later and get the heck out of there!
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